In 1938, Guy Stewart Callendar, a noted British steam engineer, published "The Artificial Production of Carbon Dioxide and Its Influence on Temperature," the first of many articles aimed at reviving the carbon dioxide theory of climate change. Callendar took his own weather observations at his home in Sussex and compiled a massive amount of temperature data from around the world. Noting an upward trend in temperatures for the first four decades of the twentieth century, he combined these results with studies of the retreat of glaciers, measurements of rising concentrations of atmospheric carbon dioxide since pre-industrial times, and information newly available concerning the infrared absorption bands of atmospheric constituents. He concluded that the trend toward higher temperatures was significant, especially north of the forty-fifth parallel; that increased use of fossil fuels had caused a rise of the concentration of CO2 in the atmosphere of about ten percent from nineteenth century levels; and that increased sky radiation from the extra CO2 was linked to the rising temperature trend. Although he was an amateur meteorologist, Callendar worked on a truly global scale, compiling a reliable world data set of surface temperatures from earliest times and insisting- long before it became fashionable to do so-that climatology must deal with physics and atmospheric dynamics. Even in the depths of World War II Callendar remained active in climate research, publishing two papers while working on technical problems (including infrared absorption) with the Ministry of Supply. In 1944 climatologist Gordon Manley noted Callendar's valuable contributions to the study of climatic change. A decade later, Gilbert Plass and Charles Keeling consulted with Callendar before beginning their research programs. Just before the beginning of the IGY, Hans Seuss and Roger Revelle referred to the "Callendar effect," defined as climatic change brought about by anthropogenic increases in the concentration of atmospheric carbon dioxide, primarily through the processes of combustion. Until recently, Callendar has been a neglected figure in the history of science. Now, his correspondence with such notables as Hubert Lamb, J. Murray Mitchell, Helmut Landsberg, and others mentioned above, and some ninety-five of his notebooks, held at the University of East Anglia, have been preserved, indexed, scanned, and are being made available to researchers as digital images. These documents contain data, charts, notes, reviews, and many candid insights into the state of climate science between 1936 and 1964. This collection is being supplemented by a set of Callendar's complete published works and by research in other archival repositories that will help provide a more complete account of the life and work of this most remarkable and dynamic climatologist.